1. Field of the Invention
This invention relates to a method for cooling an article using a cryocooler and the cryocooler.
2. Description of the Related Art
In a superconducting filter of IT communication field, a superconducting MRI of medical field, or in fundamental scientific field, it is required to cool a high precise electron microscope or a high performance precise instrument such as a high sensitivity submillimeter wave detector or an infrared ray detector to eliminate thermal disturbances therefrom. In cooling such a high performance precise instrument as mentioned above, as of now, a liquefied gas or a cryocooler is employed. Recently, the cooling temperature range of the cryocooler is improved down to 4K, which can be easily operated by pushing a button and in the past, can be realized only by using an extremely low temperature cryogen.
FIG. 1 is a structural view schematically illustrating a conventional GM (Gifford McMahon) type cryocooler. The cryocooler 10 illustrated in FIG. 1 includes a compressor 11 and a cryocooler cold head 12. In the cryocooler cold head 12 are provided a regenerator 13 and a displacer 14, and at the bottom in the cryocooler cold head 12 is provided a cold end 16. The combination of the regenerator 13 and the displacer 14 is called as a cooling cylinder. A high pressure gas and a low pressure gas are supplied to the cryocooler cold head 12 from the compressor 11 through the flexible hoses 15 and via the switching valve 17, compressed and expanded at the cryocooler cold head 12.
At the displacer 14, cooling power is created through the expansion of the gas to be synchronized with the expansion of the gas at the next stage by operating the motor 18. The coolant is repeatedly created through a plurality of expansions of the gas, and the thus obtained cooling power is are stored in the regenerator 13. As a result, the cold end 16 is cooled down to an extremely low temperature. An article is contacted with the cold end 16 to be cooled.
FIG. 2 is a structural view schematically illustrating a pulse tube type cryocooler. The cryocooler illustrated in FIG. 2 includes a compressor 21 and a cryocooler cold head 22. In the cryocooler cold head 22 are provided a regenerator 23 and a pulse tube 24, and at the bottom in the cryocooler cold head 22 is provided a cold end 26. The combination of the regenerator 23 and the pulse tube 24 is called as a cooling cylinder. A high pressure gas and a low pressure gas are supplied to the cryocooler cold head 12 from the compressor 21 through the flexible hoses 25 and via the switching valve 27, compressed and expanded at the cryocooler cold head 22.
At the pulse tube 24, cooling power is created through the expansion of the gas to be synchronized with the expansion of the gas at the next stage by operating the switching valve. The gas expansion is carried out by controlling the introduction timing of the gas into a buffer tank 28, which is successive to the pulse tube 24, via an orifice 29. The cooling power is repeatedly created through a plurality of expansions of the gas, and the thus obtained cooling power is stored in the regenerator 23. As a result, the cold end 26 is cooled down to an extremely low temperature. An article is contacted with the cold end 26 to be cooled.
In both of the GM type cryocooler and the pulse tube type cryocooler, since the high pressure gas and the low pressure gas, which are supplied from the compressors 11 and 21, are circulated in the cryocooler cold heads 12 and 22, the cold ends 16 and 26 are vibrated inevitably by an amplitude of about 10 μm in the axial directions thereof. The allowable limit in vibration of the high performance precise instrument is within a range of submicro-meter, so that if a relatively large vibration is applied to the precise instrument, the inner structure and the conrollability of the precise instrument may be destroyed, so that the precise instrument may malfunction.